The invention relates to a booster for a digital hydraulic controller and a method for using a booster in connection with a digital hydraulic controller.
Digital hydraulic controller is used in a system based on digital hydraulics, in at least part of the components is based on digital valves that form digital valve groups. A digital valve group is a valve unit, in which there is at least one digital valve group, which again contains a number of digital valves connected in parallel in relation to the fluid flow passing through the digital valve group. A digital valve again is the valve intended for adjusting the fluid's volume flow, the valve having 2−N different stepped discrete adjustment modes, especially 2 different discrete adjustment modes (open/closed), and for which the control signal to be brought from the control system has advantageously been digitalized, such as binary form. The digital valve has advantageously two modes; it is either fully open or fully closed. When the digital valve is open, the entire volume flow of liquid allowed by the digital valve passes through it, and when the digital valve is closed, no liquid at all passes through it. Such a digitally controllable digital valve having two modes is also called an on/off valve and an on/off digital valve. The digital valve can also have more than two modes, in which case the valve is driven in a stepped manner from one mode to another. The digital valve can have three positions; it lets the liquid flow pass to a first or second direction, or then the valve does not allow any fluid to pass through it. The adjusting directive (control signal) is of a digital nature, such as binary. According to the adjusting directive, the volume flow from the digital valve group and the pressure caused by the flow are adjusted by opening a certain valve combination of the digital valve group so that a desired opening of the digital valve group and a desired volume flow of the fluid are achieved. Deviating from an analogue valve, each digital valve connected in parallel can only have a limited number of adjusting modes, i.e. the digital valve only has certain discrete flowing modes. In one digital valve form, it has three modes: open/closed/quick opening. However, each digital valve preferably has simply the on/off mode; when open, the valve lets a certain volume flow through it; when closed, it completely prevents the fluid from passing through. The digital valve group consists of digital valves with two modes (on/off). Typically two successive digital valves with nominal volume flow amounts, the volume flow passing through the valve with bigger nominal volume flow in the open position is always two times bigger than the volume flow of the valve with smaller nominal volume flow. A binary control signal can then be brought to such a digital value group, in which the control signal's magnitude has been converted into a binary number. As an exemplary comparison of differences in the adjustment method between an analogue valve and a hydraulic valve group, the following can be presented: if an analogue valve is adjusted with a control signal (adjusting directive), the magnitude of which is 12 units, the analogue valve stem moves a quantity comparable with 12 control units, in which case the valve lets through a volume flow that has increased respectively. Again, when a digital valve group consisting of five on/off digital valves connected in parallel to the input flow are controlled by a similarly dimensioned control signal (adjusting directive) of 12 units, in which the sizes of the volume flows the digital valves 1, 2, 3, 4, 5 let through are respectively 1, 2, 4, 8 and 16 units, the control signal is binary and sent into a control signal 01100 (0×24+1×23+1×22+0×21+0×20=12) (corresponding to the valves 5, 4, 3, 2, 1), and the valves 3 and 4 are opened. Controllers for controlling digital hydraulics thus comprise a set of on/off valves which are connected in parallel and extend between an input line and an output line and for example for pressure control the controller has two sets of valves in which one set connects a feed line to an output line of the controller and other set connects the output line to a drain line.
In patent application DE 102009026604 is described a hydraulic cylinder assembly for a machine for producing a fiber web, especially a paper or cardboard making machine. This prior art assembly comprises a hydraulic cylinder having a cylinder housing and a piston which can be displaced inside the cylinder housing, said piston subdividing the cylinder housing into a chamber on the cylinder head side and a chamber on the cylinder back end side and at least one digital hydraulic pressure controller which is integrated into the assembly. The pressure controller is associated with the chamber on the cylinder head side and the chamber on the cylinder back end side and controls a supply of working fluid to and a discharge thereof from the chambers to adjust the pressure of the working fluid in at least one of the chambers of the hydraulic cylinder. This prior art publication teaches that important for the quality of the hydraulic control using digital controllers is the switching speed of individual valves that means how fast the valves can be opened or closed. For rapid movements of the valve body in the valve also great forces are needed to hold the valve in the controlled state. For this purpose boosters or amplifiers are suggested in order to provide the coil of the electromagnetically actuated valve fast switching so that a stronger magnetic field is produced and the valve body can be moved fast. Problematic in this prior art document is that it does not give any actual examples as how to provide the hydraulic cylinder assembly with digital valves with such a booster or amplifier neither is such available commercially.
An attempt is known to the applicant in which the booster was provided with one channel and a special coil was used with 24 V input voltage located inside but this attempt proved not to function. Thus there is no practical solution available to be used in connection with commercially available digital valves in connection with normal automation system. Thus the problem of rapid enough state change of a digital valve is unsolved in prior art.